1. Field of the Invention
The present invention relates to an air filter or air cleaner. More particularly, it relates to a porous adsorbent highly capable of removing aldehydes, in particular lower aldehydes such as formaldehyde and acetaldehyde, contained in a gaseous phase therefrom.
2. Prior Art
Various adsorbents have so far been developed for the purpose of removing odor components occurring in the living environment and working environment. In recent years, the problems of odor and odor hazards have attracted attention from the viewpoint of further improvement in the living environment and working environment and the adsorbent of an agent capable of more effectively eliminating lower aldehydes, such as formaldehyde and acetaldehyde, in particular, among those odor components has been earnestly waited for.
In the art, such porous adsorbents as activated carbon, activated clay, silica gel and activated alumina, in particular porous adsorbents with activated carbon as a support, have been used in most cases for removing lower aldehydes. These adsorbent, however, have drawbacks; they are low in adsorbent capacity for lower aldehydes and the duration of their adsorbing power, namely their life, is short.
As means of making improvements in these respects, there have also been proposed various adsorbents whose adsorbent capacity for lower aldehydes is increased by carrying various organic or inorganic compounds on porous carriers or supports. Thus, in Japanese Patent Publication 54095/1985, Japanese Laid-Open Patent 159836/1980, Japanese Laid-Open Patent 48138/1985, Japanese Laid-Open Patent 358536/1992 and Japanese Laid-Open Patent 285619/1999, there are proposed adsorbents which comprise organic compounds reactive with lower aldehydes, for example aniline, hydrazines, aliphatic primary or secondary amines, saturated cyclic secondary amines or ureas, fixed or immobilized on a porous adsorbent such as activated carbon. Also proposed are adsorbents comprising inorganic compounds, such as acidic ammonium salts, sulfite salts, metal oxides, metal sulfates, metal acetates or metal carboxylates, carried on a porous support such as activated carbon and, further, adsorbents derived from the above-mentioned adsorbents by causing a platinum compound to be supported thereon as a catalyst.
However, those adsorbents which carry organic compounds are unstable in adsorbent capacity, namely their adsorbent capacity changes with the lapse of time, and they further have the problem that their odor, among others, is harmful to humans. Another disadvantage of these adsorbents carrying organic compounds is that they are poor in heat resistance. In addition, they cannot be said to be satisfactory from the rate of adsorption viewpoint.
On the other hand, adsorbents carrying an inorganic compound are also known. However, these are generally insufficient in rate of adsorption., Those carrying a catalyst such as a platinum compound are disadvantageous in that they are poor in adsorbent capacity at ordinary temperature. As discussed hereinabove, the adsorbents so far proposed can hardly be said to be satisfactory in eliminating lower aldehydes. Accordingly, it is an object of the present invention to provide an adsorbent which can remove lower aldehydes at ordinary temperature with high efficiency for a prolonged period of time and which is excellent in removal rate, heat resistance and safety.
The present inventors made intensive investigations in an attempt to accomplish the above object and have now completed the present invention. Thus, the invention provides a porous adsorbent which comprises a urea compound having a urea linkage within the molecule thereof and an inorganic acid and/or an organic acid, each carried on a porous carrier or support. In another aspect, the present invention provides a filter formed from the above porous adsorbent.